We conducted a distributional survey of Pectinatella magnifica, an invasive species, in the Geum River and the Nakdong River from July 12 to July 25, 2014. The spacing between the study sites was 10 km along the main channels for the Geum River (n = 12, 120 km) and the Nakdong River (n = 38, 380 km) from the estuarine barrage to upper part of main channel. Pectinatella magnifica was detected along the riparian zone (within 100 m) at each of the study sites. Presence rate of P. magnifica in Geum River and Nakdong River was 25% and 32.6%, respectively. The colony number of P. magnifica at Geum River ($9.5{pm}3.1colony/m$, n = 3) was over 94 fold higher than that in the Nakdong River ($0.1{pm}0.1colony/m$, n = 16). The Total length distribution of P. magnifica had a truncated bell shape at each rivers (mean length: $14.0{pm}1.2cm$ for Geum River (n = 32), and $16.8{pm}1.4cm$ for Nakdong River (n = 52)). These findings could provide basic information regarding the distribution pattern of P. magnifica in a new invasion area.